A fertilized egg will implant itself in a woman's uterus six to 12 days after conception. At this stage, the woman's body begins to change immediately. The pregnancy hormone human chorionic gonadotropin, or hCG, develops and levels of this hormone begin to rise in the blood stream. An hCG test can determine if a woman is pregnant, diagnose if a pregnancy is failing, and monitor a pregnancy in trouble, according to LabTestsOnline.
Qualitative hCG
Qualitative hCG is used to confirm pregnancy; its results are returned simply as positive if the woman is pregnant or negative if she is not. Qualitative hCG measures the amount of hCG in the blood. In non-pregnant women, hCG levels are normally undetectable. In pregnant women, the level of hCG begins to rise at implantation and should increase every 48 to 72 hours over the next several weeks.
Ectopic Pregnancy
A series of hCG tests performed over several days may be ordered to rule out ectopic pregnancy, or a pregnancy where the egg has implanted in a Fallopian tube instead of in the uterus. MayoClinic.com notes up to an estimated 20 or every 1,000 pregnancies are ectopic. An egg cannot develop outside the uterus, and the ectopic tissue must be removed. An ectopic pregnancy would show hCG levels that start out normal but fail to show a significant rise or stop rising completely, according to the American Pregnancy Association.
Doubling Time
Levels of hCG rise at various rates throughout the pregnancy. During early pregnancy, hCG levels double every two to three days until hCG reaches 6,500 mIU/ml, at about the eighth week after the missed menstrual cycle. Ectopic pregnancies will usually have a longer doubling time. Failing pregnancies will also show a longer doubling time and may even return a slowly declining level of hCG. A miscarriage will show a sharp decline in hCG.
Five Weeks
Levels of hCG should be between 18 and 7,340 mIU/ml at five weeks into the pregnancy. Some type of fetal development should be seen on an ultrasound when hCG levels reach at least 2,000 mIU/ml.
Eight Weeks
At about the eighth week of pregnancy, hCG levels become more individualized, peaking between the 60th and 70th days of gestation. Levels may drop slightly between the 12th and 16th week and then remain constant until birth.
Test
This test may be performed on the patient's blood or urine. There is no special preparation for an hCG blood test--the patient may eat or drink normally. The patient should avoid drinking excessive amounts of water before submitting a urine specimen for hCG testing, as this might dilute urine and deliver a false negative reading, according to LabTestsOnline.org.
